More 516 prep (rename caller vars)

[Absolucy]

About The Pull Request

Caller is a protected/reserved var in 516, and it's used in various places, so let's... fix that:

- caller and callee vars

	- The current proc has caller and callee vars that return a reference to
	  the running caller and to the running proc itself, respectively. The
	  returned var is of internal type /callee.

	- /callee has vars src, usr, args, file, line, caller, and all vars that
	  apply to proc prototypes (name, type, desc, category, invisibility).	 

yes I did just a find & replace

no I'm not adding // monkestation edit next to these edits, /tg/ will end up doing the same thing anyways

Why It's Good For The Game

so 516 compiles lol

Changelog

No user-facing changes (only renames variables)